Christine Rehm

Kookaburra: the ultra-small-angle neutron scattering instrument at OPAL

The new double crystal ultra-small-angle neutron scattering instrument Kookaburra, currently under construction at the ANSTO OPAL reactor, will allow characterization of microstructures covering length scales in the range of 0.1 to 10 µm. Using the 002 and 004 reflections of a doubly curved mosaic highly oriented pyrolytic graphite premonochromator crystal at a fixed Bragg angle of 45° in conjunction with two pairs of Si(111) and Si(311) quintuple-reflection channel-cut crystals will allow operation of the instrument at two different wavelengths, thus optimally accommodating weakly and strongly scattering samples in one sample position. The versatility, the estimated neutron fluxes and the low background noise of Kookaburra suggest that this state-of-the-art instrument will have a major impact in the field of large-scale structure determination.

Polymeric Ionic Liquid Nanoparticle Emulsions as a Corrosion Inhibitor in Anticorrosion Coatings

In this contribution, we report the facile preparation of cross-linked polymerizable ionic liquid (PIL)-based nanoparticles via thiol–ene photopolymerization in a miniemulsion. The synthesized PIL nanoparticles with a diameter of about 200 nm were fully characterized with regard to their chemical structures, morphologies, and properties using different techniques, such as Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. To gain an in-depth understanding of the physical and morphological structures of the PIL nanoparticles in an emulsion, small-angle neutron scattering and ultra-small-angle neutron scattering were used. Neutron scattering studies revealed valuable information regarding the formation of cylindrical ionic micelles in the spherical nanoparticles, which is a unique property of this system. Furthermore, the PIL nanoparticle emulsion was utilized as an inhibitor in a self-assembled nanophase particle (SNAP) coating. The corrosion protection ability of the resultant coating was examined using potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that the PIL nanoparticle emulsion in the SNAP coating acts as an inhibitor of corrosion and is promising for fabricating advanced coatings with improved barrier function and corrosion protection.

Investigating linear and nonlinear viscoelastic behaviour and microstructures of gelatin-multiwalled carbon nanotube composites

We have investigated the linear and nonlinear rheology of various gelatin-multiwalled carbon nanotube (gel-MWNT) composites, namely physically-crosslinked-gelatin gel-MWNT composites, chemically-crosslinked-gelatin gel-MWNT composites, and chemically–physically-crosslinked-gelatin gel-MWNT composites. Further, the internal structures of these gel-MWNT composites were characterized by ultra-small angle neutron scattering and scanning electron microscopy. The adsorption of gelatin onto the surface of MWNT is also investigated to understand gelatin-assisted dispersion of MWNT during ultrasonication. For all gelatin gels, addition of MWNT increases their complex modulus. The dependence of the storage modulus with frequency for gelatin-MWNT composites is similar to that of the corresponding neat gelatin matrix. However, by incorporating MWNT, the dependence of the loss modulus on frequency is reduced. The linear viscoelastic region is decreased approximately linearly with the increase of MWNT concentration. The pre-stress results demonstrate that the addition of MWNT does not change the strain-hardening behaviour of physically-crosslinked gelatin gel. However, the addition of MWNT can increase the strain-hardening behaviour of chemically-crosslinked gelatin gel, and chemically–physically crosslinked gelatin gel. Results from light microscopy, cryo-SEM, and USANS demonstrate the hierarchical structures of MWNT, including that tens-of-micron scale MWNT agglomerates are present. Furthermore, the adsorption curve of gelatin onto the surface of MWNT follows a two-stage pseudo-saturation behaviour.

DCD USANS and SESANS: a comparison of two neutron scattering techniques applicable for the study of large‐scale structures

This paper provides a comparison of the capabilities of two techniques for extending the range of conventional small-angle neutron scattering (SANS) towards the micrometre length scale, namely the double-crystal diffraction ultra-small-angle neutron scattering (DCD USANS) technique, which uses perfect silicon crystals in Bragg reflection, and spin-echo SANS (SESANS), a method that uses the spin precessions of a polarized neutron beam. Both methods encode the scattering angle to very high precision. Based on round-robin test measurements, the strengths and weaknesses of the two techniques are discussed with respect to the measurement of the particle size of monodisperse scatterers, and potential performance gains for state-of-the-art DCD USANS and SESANS instruments are investigated.

Design and performance of the variable-wavelength Bonse–Hart ultra-small-angle neutron scattering diffractometer KOOKABURRA at ANSTO

The double-crystal ultra-small-angle neutron scattering (USANS) diffractometer KOOKABURRA at ANSTO was made available for user experiments in 2014. KOOKABURRA allows the characterization of microstructures covering length scales in the range of 0.1–10 µm. Use of the first- and second-order reflections coming off a doubly curved highly oriented mosaic pyrolytic graphite premonochromator at a fixed Bragg angle, in conjunction with two interchangeable pairs of Si(111) and Si(311) quintuple-reflection channel-cut crystals, permits operation of the instrument at two individual wavelengths, 4.74 and 2.37 A. This unique feature among reactor-based USANS instruments allows optimal accommodation of a broad range of samples, both weakly and strongly scattering, in one sample setup. The versatility and capabilities of KOOKABURRA have already resulted in a number of research papers, clearly demonstrating that this instrument has a major impact in the field of large-scale structure determination.

Characterization of porosity in sulfide ore minerals: A USANS/SANS study

Abstract Porosity plays a key role in the formation and alteration of sulfide ore minerals, yet our knowledge of the nature and formation of the residual pores is very limited. Herein, we report the application of ultra-small-angle neutron scattering and small-angle neutron scattering (USANS/SANS) to assess the porosity in five natural sulfide minerals (violarite, marcasite, pyrite, chalcopyrite, and bornite) possibly formed by hydrothermal mineral replacement reactions and two synthetic sulfide minerals (violarite and marcasite) prepared experimentally by mimicking natural hydrothermal conditions. USANS/ SANS data showed very different pore size distributions for these minerals. Natural violarite and marcasite tend to possess less pores in the small size range (<100 nm) compared with their synthetic counterparts. This phenomenon is consistent with a higher degree of pore healing or diagenetic compaction experienced by the natural violarite and marcasite. Surprisingly, nanometer-sized (<20 nm) pores were revealed for a natural pyrite cube from La Rioga, Spain, and the sample has a pore volume fraction of ~7.7%. Both chalcopyrite and bornite from the massive sulfide assemblage of the Olympic Dam deposit in Roxby Downs, South Australia, were found to be porous with a similar pore volume fraction (~15%), but chalcopyrite tends to have a higher proportion of nanometer-size pores centered at ~4 nm while bornite tends to have a broader pore size distribution. The specific surface area is generally low for these minerals ranging from 0.94 to 6.28 m2/g, and the surfaces are generally rough as surface fractal behavior was observed for all these minerals. This investigation has demonstrated that USANS/SANS is a very useful tool for analyzing porosity in ore minerals. We believe that with this quantified porosity information a deeper understanding of the complex fluid flow behavior within the porous minerals can be expected.

KOOKABURRA: The Ultra-Small-Angle Neutron Scattering Instrument at ANSTO

Volume 27 • Number 2 • 2016 Neutron News 30 Introduction The KOOKABURRA ultra-small-angle neutron scattering (USANS) instrument [1] as shown in Figure 1 is located upstream of the PLATYPUS neutron refl ectometer [2,3] on OPAL’s cold-neutron guide CG3 [4]. KOOKABURRA is based on the classical Bonse-Hart method [5], which uses two multiple-refl ection, perfect Si channel-cut crystals (labelled monochromator and analyser) arranged in a nondispersive geometry to achieve a steep decrease in the tails of the perfect crystal diffraction rocking curves. This technique permits the detection of very small angular deviations of the neutron beam after scattering from a sample placed between the monochromator and analyser crystals [6]. At ANSTO, KOOKABURRA extends the range of experimentally measurable length scales accessible with the small-angle neutron scattering (SANS) instruments QUOKKA [7] and BILBY (refer to article elsewhere in this Neutron News edition) by up to two orders of magnitude into the micrometre regime. Thus, multilevel structures in solids and liquids, containing not only nanometre-sized molecules and particles but also micrometre-sized aggregates and agglomerates, can be probed via neutron scattering. USANS is useful for studies of pores and cracks in rocks, cement or engineerKOOKABURRA: the ultra-small-angle neutron scattering instrument at ANSTO

Insights into Free Volume Variations across Ion-Exchange Membranes upon Mixed Solvents Uptake by Small and Ultrasmall Angle Neutron Scattering

Ion-exchange membranes are composite separation materials increasingly used in a variety of electro-membranes and electrochemical processes. Although promising for solvent reclamation, to date, their main applications are limited to aqueous environments due to physicochemical and microstructural changes of the materials upon exposure to nonaqueous and mixed solvents solutions, affecting long-term stability and separation performance. In the present work, the structural changes of commercial and novel hybrid ion-exchange membranes in mixed methanol/water and ethanol/water solutions are assessed for the first time using ultra- and small-angle neutron scattering techniques. The interface between the ion-exchange functional layer and the mechanical support of the membranes is evaluated in the ultralow-q region, while a broad solvent-dependent peak at the mid-q region was correlated to the microstructural properties which are related to the free volume across the ion-exchange domains and to the materials electrical and nanoscale mechanical properties. The results of this study may offer new opportunities toward the development of an efficient separation process using ion-exchange membranes for the purification of fermentation broths toward biofuel generation.

Micron-scale restructuring of gelling silica subjected to shear

HYPOTHESIS/OBJECTIVE We examine the time dependent viscometric behavior of a well-defined system of gelling colloidal silica and how this behavior may be understood from a simple theoretical model which incorporates the microstructure of the gel. The ultra-small angle neutron scattering (USANS) technique is used to interrogate structure during the gelation process. EXPERIMENTS The investigations focused on a system where both particles and interactions are well-defined: 7 nm silica particle acid-treated aqueous solution subjected to a constant applied shear in Couette geometry. Ultra-small angle neutron scattering (USANS) time-dependent scattering intensities were measured at wave vectors, q, in the range, 1.0 × 10-3 ≤ q/nm ≤ 7.3 × 10-2 coupled with viscosity data recorded simultaneously. The interpretation of the USANS scattering data is reliant on an isotropic sample. This assumption has been investigated, over a limited range of scattering vectors, using more suitable small angle neutron scattering (SANS) instrumentation with a restricted q-range. FINDINGS The first recorded direct kinetic measurements of the micron-scale structure in a gelling system. A critical micro-structural feature of the intensity-viscosity time behavior of a gelling colloid subjected to a shear is the cluster size. A viscosity/intensity coupling observed at the time of a viscosity maximum that corresponds to a time-dependent critical stress and speculated to be independent of the wave vector over a wide q-range.

Structural evolution of photocrosslinked silk fibroin and silk fibroin-based hybrid hydrogels: A small angle and ultra-small angle scattering investigation

Regenerated Bombyx mori silk fibroin (RSF) is a widely recognized protein for biomedical applications; however, its hierarchical gel structure is poorly understood. In this paper, the hierarchical structure of photocrosslinked RSF and RSF-based hybrid hydrogel systems: (i) RSF/Rec1-resilin and (ii) RSF/poly(N-vinylcaprolactam (PVCL) is reported for the first time using small-angle scattering (SAS) techniques. The structure of RSF in dilute to concentrated solution to fabricated hydrogels were characterized using small angle X-ray scattering (SAXS), small angle neutron scattering (SANS) and ultra-small angle neutron scattering (USANS) techniques. The RSF hydrogel exhibited three distinctive structural characteristics: (i) a Porod region in the length scale of 2 to 3nm due to hydrophobic domains (containing β-sheets) which exhibits sharp interfaces with the amorphous matrix of the hydrogel and the solvent, (ii) a Guinier region in the length scale of 4 to 20nm due to hydrophilic domains (containing turns and random coil), and (iii) a Porod-like region in the length scale of few micrometers due to water pores/channels exhibiting fractal-like characteristics. Addition of Rec1-resilin or PVCL to RSF and subsequent crosslinking systematically increased the nanoscale size of hydrophobic and hydrophilic domains, whereas decreased the homogeneity of pore size distribution in the microscale. The presented results have implications on the fundamental understanding of the structure-property relationship of RSF-based hydrogels.